Liquid aerosol indicating apparatus



March l, 1960 sof s/ F. w. B'Qo'rH 2,926,521 LIQUID AERosor. mmcATING APPARATUS v Filed April 21. 1958 Z.: E. l Tl. Z U ,2 29

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INVENTOR FRANKLIN w. BooTH ATTORNEY nite The invention described herein may be manufactured and used by vor for the Government of the United States of `America for 'governmental purposes without the. payment of any royalties thereon or therefor.

This invention relates to apparatus for continuous or intermittent measurement of a suspension of liquid particles in a gas, usually known as liquid aerosols, particularlyV aerosols in a condition of supersaturation in a gas stream at gas pressures varying from sub-atmospheric to super-atmospheric pressures.

In many manufacturing processes it has become important to determinethe mass of liquid in aerosols which are subject to varying pressures, such as condensed water vapor in air upstream and downstream of liquid moisture separators or in air entering silica gel or activated alumina air dryers.

In my copending application Serial No. 619,646, filed October 31, 1956, of which this application is a continu tion-in-part, there is disclosed a liquid aerosol indicator which, while capable of producing excellent results in aerosol mass determination, is subject to leakage under certain conditions of use, and non-uniform control .of aerosol ow at the intake valve due to improper coaction of the screw cone valve member with the non-planar valve seat in the inflow duct. A further deficiency in one embodiment of the prior device for some uses arises in the expansion chamber of the apparatus where use is made of liquid containingy thermometers, the mixing of the wet and dry gases producing inaccuracies in the indications, since the separate ducting for wet and dry bulbftliermometers `doeswnot allow the gas which has received moisture from the'wick of the wet bulb Ythermom'eter, andy is cooled thereby, to impinge on dry bulb thermometer giving a'false dry bulb reading.

It is accordingly an important object of the invention to provide apparatus for mass measurement of liquid aerosols wherein complete and accurate control lover the aerosol intake is provided. An object also is to insure accuracy in mass measurement of the indicator using liquid wet and dry bulb thermometers by preventing impingement of wet bulb gases on the dry bulb thermometer. An additional object is to provide .apparatus for liquid aerosol measurement `which is of simplified construction reducing difliculty and expense of manufacture, which may be of small size and which may be readily manipu-Y lated for quantitative determinations.

Other objectsand many of the attendant advantages of this invention will be readily appreciated as the same becomes'better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

n m od'me o the'n- Fig 1 1S a secuonal View of an e b l nt f l t ls'the dry thermometer-50. This thermometer 1s shown as vent'ion showing the leak resistant valve structure;

Fig. 2 is a view similar to Fig. 1 but illustrating the use offliqid type thermometers with separators for preventing intermixing of d'ry bulb and wet bulb gases; and Fig. 3 shows the apparatus of Fig. 2 without the heaters l taes Patent 2,926,521 iatented Mar. l, 196Q The apparatus as shown in Fig. 1 includes ametal tting 10 which may be hexagonal in section for easy screw attachment, the ends 11 and 12 of the tting being externally screw threaded for attachment to the aerosol container and to the expansion tube 13 of the apparatus respectively. Flow space through fitting 10 is comprised in two ducts 15 and 16, duct 15 at the axial center of screw 'end 12 and duct 16 Vdisplaced transversely from the axial center of screw end 11 and of smaller'diameter than duct 15, both ducts extending in parallel relationship in the body of the fitting to overlap each other as shown in the figure. Pitot tube 14 is pressed into an en# largement of the open end of duct-16. A bridging duct 17 of larger diameter than duct 16 is formed between ducts 15 and 16, the bridging duct forming a valveirecess and the periphery of duct 17 adjoining duct 15 forming the seat for thertapered end 18 of screw valve 20, mounted radially in the wall of the center section 21 of fitting 10. The upper end of duct' 15 is liared outwardly in an exit cone 19 having a terminal edge adijacent Athe outer wall of fitting section 12. Between the external thread of fitting section 12 and center section' 21 an annular groove 22 is cut in the fitting surface; and the expansion tube 13 has one end internally threaded to engage the outer thread on fitting section 12, the tube edge being tapered on its inner side to form a pressure surface 25 for engaging a sealing gasket 26 placed in fitting groove 22, whereby a tight gas fit between these parts is secured. v

The tube 13 forms an expansion chamber which is divided internally into three separate but connecting cells or compartments, namely, a heating cell 27, adjacent the attachment section 12 of fitting 10, a dry thermometer cell 28, and a wet thermometer cell 29, these cells being connected in sequence. The terms wet and dry are used instead of wet bulb and "dry bulb in describ ing the thermometers since they are of the electrical thermocouple type.y The cell 27 contains an electric heating element 3i) which is in the form of an open ended tube containing a bare electrical conductor connected at its ends to lead-out wires 32 and 33. Each lead-out wire is supported by a terminal member 34 consisting of a stainless steel plug 35 having a central bore adapted to receive the wire-insulating tub'e'vltti'.V The plugs 35 are inserted in openings formed in the wall of the tube cell 2'7 adjacent the endsV of heating element 30, with the plug wall welded to the edge of the enclosing opening. The inner plug end terminates iiush with the inner surface of the shell and the heater( 30 is electrically insulated from the cell wall by insulation Washers 38. 'l

The dry thermometer cell 28 has a diameter slightly less than the heater cell 30 and the wet thermometer cell29,` permitting formation of ledges 40 and 41 at the ends'f the dry thermometer cell 28, ledge 4t) serving to supprt nozzle 43 and ledge 41 supporting screen 44. Nozzle 43: is in the form of a centrally apertured disk held in position 'by set screw 46 in the cell wall with the screw end seated in a recess formed in the nozzle wall. vThe nozzle orilice or aperture, for half its length from the wet thermometer space, is cylindrical in shape, as at 47, the other half, 4S, being ared outwardly to form a converging conical surface for fluid flow. The screen 44 is fixed at its edges, by any suitable means, to the ledge 41.

Penetrating the wall of cell 28, adjacent the nozzle 40,

of the electrical type, including a tube 51, enclosing a thermocouple, positioned in and extending inwardly and outwardly from the wall opening, the inner tube end ter-- minating at about the cell center. The tube is welded t0.:

the cell wall atthe juncture of tube and wall. The

thermocouple connects with a power source and an appropriate indicator through wire connectors 54.

In the wet thermometer' cell 29, an opening 60 is made inr the wall for insertion of the wet thermometer 61 at a pointA spaced sufficiently from the dry thermometer to prevent inaccurate readings of both instruments. This thermometer is, also, of the thermocouple type, and includes the-connecting thermocouple wires and thermocouple tube 62, the latter being supported, with its thermocouple end 63 penetrating opening 60, by passing the tube through an opening in the outer'wall 64 of a box-like casing 65 integral with main tube 13, the tube 62 being electrically welded to this wall at the opening. The end of tuber62 is at the approximate cell center, and enclosing this end and the included thermocouple is a wick 66, the wick material extending from. the tube end through the opening 60 and terminating at the interior base of the casing 65. The casingg 65 serves, when the apparatusis inupright position, as shown in Fig. l,` as a receptacle for wetting liquid for the thermometer, a removable plug 67 being provided at the top side for liquid supply.

A port 70 is formed in wall 64 of casing 65 near the casing base for injection of volatile liquids, suchas Freon, when measurement of these' liquids is to be made, this port being normally closed by screw plug 71. The pressure gauge 72 is attached to tube 28 in section 29, this gauge giving the expansion chamber pressure and facilitating calculation of the expansion ratio of the aerosol across valve 20. The outer end of tube 13 is externally threaded as at 73 for connection to a source of reduced pressure, which may be the suction point of a compression stage in the system.

K The operation of the apparatus is as follows. Assuming threaded end 11 of the fitting 10 is coupled to the source of super-saturated aerosol to be measured and threaded end 73 coupled to a point of pressure reduced over values prevalent in the apparatus, and assuming also that the source pressure of the aerosol is super-atmospheric, valve is manipulated to permit a sample flow of aerosol into cell 27. Here the aerosol is expanded to less than saturated conditions and heated by heater to the original intake temperature, the temperature of the gas having been reduced by expansion.l The aerosol, now expanded to an unsaturated gas and restored to the original temperature, is then drawn through the screen 44, which serves as a mixer to secure uniform mixing of gas and expanded vapor, and passed by the dry thermometer in cell 28 which indicates the dry temperature. The nozzle 43, which is replaceable to secure different fiow apertures, develops a velocity of gas impingement on the wet thermometer wick in cell 29 of such value as to produce accurate readings, the drop in temperature due to evaporation, as registered by the wet thermometer 61, giving the required wet-dry differential for calculation of the relative humidity of the gas in the usual way by use of standard tables. Given the relative humidity, the mass in grains per cubic foot may be obtained from published data, and this value is multiplied by the expansion ratio across inlet valve 20 to obtain the grains per cubic foot in the original gas stream. Where determination of gas ow is made for a volatile substance, such as Freon, the liquid Freon is injected into casing 65 through the basal port 70, with the pressure, as indicated by gauge 72, being in excess of the condensation pressure of the volatile liquid, the aerosolV gas and vapor from the test source passing through the expansion tube 29 where it is subject to heating and dry and wettemperature measurement, as in non-volatile aerosols.

` Where super-atmospheric pressure only areinvolved in the. use of the apparatus, themodified form of apparatus shown in Fig. 2 may be used, In this modification, the fitting 75 is similar to fitting 10 of Fig. 1 except, byelimination of the gas leakage problem, the fitting end 76, corresponding to screw end. 13 of Figfl is smooth-sided and press-tted into the tube 77 where it is held by set screw 78. The parts of fitting 75 are otherwise identical to those of fitting 10 of Fig,` 1 and carry the same numerals.

Tube 77 is of bre and is divided into two cells 80 and 81 by nozzle plate 82, this plate `being secured transverse to the tube in the interior thereof by set-screw 83. Two nozzles 84 and 85 are formed in plate 82 with axes parallel to the tube axis, both nozzles having a cylindrical section on the upper or thermometer side, and a aring section on the lower or heater side, nozzle 84 having the greater nozzle area. Inside cell 80, about midway between the nozzle plate 82 and the fitting 75 is interposed the electric heater 87 which is similar to heater 30 of Fig. 1, with t'ne exception of the wire terminal lead-in arrangement where, since no inflow gas leakage is involved, the terminal wires 88 are merely passed through electric insulation blocks 89 in thetube-walL.

Tube cell Slis open-ended and includes both wet and dry bulb thermometers', the wet thermometer. having a wick 96 which covers itslower end and isI led into water receptacle 97 for. liquid supply to the wick. A separator plate 90, mounted on top of nozzle plate between the two nozzles 84 and 85 and extending diametrically across the tube cell 81, projects upwardly beyond the open end of the cell, the cell wall frictionally holding the separator in place. On bothsides of the separator, suspended by elastic clips 91 and 92 fixed to the plate 90, arethe wet and dry thermometers 93 and 94. These thermometers are of the liquid type, wet thermometer' 93 being suspended above nozzle 84 and thermometer 94 above nozzle 85, there being a short space between the thermometer bases and the nozzle plate.

The operation of this formv of indicator is, in general, similar to' that of the operation of the Fig. 1 apparatus. The tapped aerosol, as controlled by valve 2t), passesthrough fitting tubes 15 and 16 and cone'19 into heating cell 27 where the expanded and cooled gas is brought back to its initial temperature. The ow then continues through the two nozzles, the nozzle forms being such as to speed the flow to values giving accurate readings, the nozzle below the wet thermometer producing a slower speed permitting adequate vapor evaporation, and since the separator extends between the two thermometers throughout their enclosed lengths, the ow of dry and wet gases isV separate and error in temperature indication duc to intermixing of wet and dry gasesis obviated.

Where the Iules Thompson effect is small or where approximate indications. only are needed the heater 87 of Fig. 2 may be omitted, as shown'in Fig. 3.' The structure of Fig. 3 is otherwise identical to thatv of Fig. 2 with theexception of the heater cell length, whichy is reduced to a smallV expansion cell 98. Fig. 3, accordingly, is, in general, numbered as in Fig. 2 to indicate identical parts.

In review, theV aerosol indicator incorporates specific improvements over related structure in that the inlet valve to the indicator, for aerosol flow, is made pressure tight, the seat of valve cone 18 permitting a close seal closure in distinction over valves wherein recess 17 is absent and the valve cone operates only in a cylindrical duct permitting substantial leakage, particularly under conditions of sub-atmospheric pressures in the test circuit. Also, in the construction of Fig. l, in both the heater and thermostats the electrical wire outlet construction has been simplified reducing costs; and inthe constructions of Figs. 2 and 3, the mixing of wet and dry gases, producing incorrect readings, is entirely prevented.

Obviously many modifications and variations of the presen-t invention are possible in theplight of the above teachings. It is therefore to be understood that within thev scope ofthe appended claims theinvention may be practicedotherwise than as specifically described. -What isV claimed` is: l

41. Apparatus for determination of the mass content mounted side' by side, parallel to the chamber axis with' in said chamber, a separator plate interposed between said thermometers transversely of said chamber, said separator plate having attachment means for supporting said thermometers in said chamber on opposite sides of the plate, and a nozzle plate positioned transversely of said chamber at the fitting ends of said thermometers,

said nozzle plate having two nozzles therein one of each of said nozzles being in line with the heat sensitive section of one of said thermometers whereby aerosol flow through said expansion chamber is passed with increased velocity toward said thermometers, said separator plate being mounted on said nozzle plate between said nozzles and extending axially in said chamber between said thermometers, whereby intermixing of the fluids on oppo site sides of said plates is prevented.

' greater than the other nozzle whereby the velocity of v 2. The apparatus as defined in claim 1, the nozzle in line with said wet thermometer having an orifice area aerosol ow by said `wet thermometer is reduced over that by said dry thermometer.

3. The apparatus as defined in claim 2 and a heater insaid chamber mounted between the nozzle plate and ttingV for heating the aerosol on emission from said fitting ducts.

4. The apparatus as dened in claim 1, and a heater in said chamber mounted between the nozzle plate and tting for heating the aerosol on emission from said ftting ducts.

References Cited in the le of this patent UNITED STATES PATENTS 1,499,433 Williston July 1, 1924 1,601,243 Irwin Sept. 28, 1926 1,620,864 Benesh Mar. 15,'1927 2,095,237 Brooks et al. Oct. 12, 1937 2,509,889 Shockley a May 30, 1950 

